The present invention relates to a liquid crystal display device, and more particularly to a so-called partial transmissive-type liquid crystal display device.
A partial transmissive-type liquid crystal display device includes a region which reflects an external light and a region which allows transmitting of light from a back light in one pixel. Such a liquid crystal display device is popularly used in an equipment which is used indoors as well as outdoors such as a mobile phone, for example. The liquid crystal display device displays images using the external light when a using environment is bright and displays images using light from the backlight when the using environment is dark (see Japanese Unexamined Patent Publication 2001-350158 (patent literature 1) for example).
Generally, the partial transmissive-type liquid crystal display device is constituted of two transparent substrates made of glass or the like which are arranged to face each other in an opposed manner with a liquid crystal layer therebetween. Then, on one transparent substrate out of two transparent substrates, a plurality of gate lines which extend in the first direction (X direction, usually horizontal direction) and are arranged in parallel in the second direction (Y direction, usually vertical direction) and a plurality of drain lines which extend in the Y direction and are arranged in parallel in the X direction are formed. A region on which the plurality of gate lines and the plurality of drain lines are formed constitutes a pixel region. In the pixel region, a plurality of pixels each of which is constituted of a switching element such as a thin film transistor or the like and a pixel electrode are formed. Then, the above-mentioned switching elements are formed in the vicinity of crossing portions between the gate lines and drain lines, and in a region which is surrounded by two neighboring gate lines and two neighboring drain lines, one pixel is formed using the above-mentioned switching element and pixel electrode. The switching element is selectively operated in response to a scanning signal supplied from the gate line, while a video signal from the drain line is supplied to the pixel electrode through the switching element.
Each pixel electrode of the partial transmissive-type liquid crystal display device is constituted of a light-transmitting pixel electrode and a light-reflecting pixel electrode which are arranged in one pixel region. One pixel electrode formed on two transparent substrates having the light transmitting property is formed of a light transmitting conductive layer such as ITO (Indium-Tin-Oxide), for example, while another pixel electrode having the light reflecting property is formed of a non-light-transmitting conductive layer such as a metal layer made of aluminum (Al) or the like.
Further, on another transparent substrate out of two transparent substrates which constitute the liquid crystal display device, a counter electrode formed of a light transmitting conductive layer is formed, wherein the counter electrode is formed in common with respective pixel regions. Then, an electric field is generated between the pixel electrode formed on one transparent substrate and the counter electrode formed on another transparent substrate, and images are displayed by turning on or off the pixel by controlling the orientation direction of liquid crystal molecules which constitute a liquid crystal layer within the pixel region in response to the electric field.
In the partial transmissive-type liquid crystal display device, an insulation film is formed over the pixel electrode formed of the light transmitting conductive layer, a light transmitting region is formed by removing a portion of the insulation film thus exposing the pixel electrode formed of the light transmitting conductive layer, and the previously-mentioned pixel electrode is formed of the non-light transmitting conductive film in the region above the insulation film and excluding the light transmitting region thus forming a light reflecting region. Further, there has been also known a multi-domain liquid crystal display element in which a common electrode made of metal such as Al is formed such that the common electrode surrounds the pixel region, and the pixel electrode and the common electrode are formed to be overlapped to each other (see paragraphs 0014-0015, 0020, 0031 of Japanese Unexamined Patent Publication 2000-194016 (patent literature 2)).